It is really difficult to answer your question as you have not told us - at least not where I am looking - what car you want to work on.
Assuming the eBay cable is compatible and will talk with your car and your computer - not a given - then you should be able to buy a license and do all you want to do.
Again, to confirm, we would need to know what car (Model, Year and so on).
You could also ask the eBay vendor about compatibility with your car.
I'd be glad to tell you which of the genuine leads would be best for your car once I know what that car is.